Stator vane assembly having composite sectors



CTORS June 20, 1967 STATOR VANE ASSEMBLY HAVING COMPOSITE SE 2 Sheets-Sheet 1 Filed Dec. 6, 1965 INVENTOR. fi WZZV/A/ 5450 flaky. 1Q. p-waw {rial/16y- June 20, 1967 M. 5080 3,326,523

STATOR VANE ASSEMBLY HAVING COMPOSITE SECTORS Filed Dec. 6, 1965 2 Sheets-Sheet INVENTOR. flfZW/V 596, 0 BY United States Patent 3,326,523 STATOR VANE ASSEMBLY HAVING COPAPGSITE SECTORS Melvin Boho, Topsfield, Mass, assignor to General Electric Company, a corporation of New York Filed Dec. 6, 1965, Ser. No. 511,962 8 Claims. (Cl. 253-78) This invention relates to stator vane assemblies for axial flow turbomachines and, more particularly, to a stator vane assembly having composite stator vane sectors combining both superior vibration damping characteristics and a high degree of wear resistance.

In axial flow turbomachines, especially axial flow compressors of aircraft gas turbine engines, there are two common ways of assembling non-variable, or fixed angle, stator vanes. These two common types of construction are the individual base type and the sector type. In the individual base type of construction, each stator vane has its own base and each base is individually supported in the compressor. More particularly, it is typical in this type of construction to provide each base with support lugs which are received in a suitable support means such as a T-shaped slot in the compressor casing, the bases of adjacent vanes abutting in the support slot. In the sector type of construction, there is a common base member for a plurality of vanes, each vane being rigidly secured to the base member which is then supported in the compressor.

It is Well known that stator vanes are often subject to vibration during high speed turbomachine operation. While the causes of this vibration, as well as its nature, are not always fully understood even by those highly skilled in the art, it is clear that such vibration is caused primarily by non-uniform aerodynamic forces acting on the vanes during operation. Even a theoretically smooth flow, such as that expected in an axial flow compressor, may actually be quite irregular and may cause forced and synchronous vibration in the stator vanes. If sufiiciently severe, such vibration can create extremely high stresses in the vanes and can ultimately cause fatigue failure. To prevent such failure, it is desirable to provide suitable means for damping the destructive vibration. Actually, the individual base type of stator construction has extremely effective internal damping characteristics due to movement of the individual bases in the support structure and relative to each other. As a result of this movement, substantial amounts of energy are dissipated through the frictional rubbing which occurs both between the individual bases and the support structure and between adjacent bases at their abutting surfaces. It has been found in practice, however, that this relative movement can result in uneven and sometimes excessive wear on the support lugs of the individual bases. On the other hand, the sector type of stator vane construction generally exhibits very little wear on the common base member due both to relatively little motion between the common base member and its support structure and to relatively uniform loading on the support portions of the base member. As would be expected, however, this low wear is usually accompanied by very little damping in the system. Furthermore, the sector type of construction is quite often expensive and difficult to manufacture, particularly of certain materials such as titanium. In addition, failure of a small portion of the sector, such as failure of a single vane, necessitates the removal and replacement of the entire stator vane sector.

It is therefore an object of this invention to provide an improved stator vane assembly having the advantages, but not the disadvantages, of both common types of stator construction. 7

Another object of this invention is to provide a stator vane assembly having a high degree of wear resistance in combination with superior vibration damping characteristics.

A further object is to provide for turbom-achines an improved stator vane assembly which is not only effective in resisting wear, but also relatively inexpensive and easy to manufacture and maintain.

Briefly stated in carrying out the invention in one form, a stator vane sector is comprised of a plurality of stator vanes having discrete base portions held in abutting relationship by means frictionally engaging the base portions and providing vibration damping. The abutting base portions form a composite arcuate base which is supported in a turbomachine as a discrete member. In accordance with an illustrated embodiment of the invention, the means frictionally engaging the base portions is a stressed member resiliently mounted in a continuous groove formed in the composite base.

By a further aspect of the invention, the individual base portions have lugs thereon which cooperate to form composite flanges which are engaged by suitable support means forming an integral portion of the turbomachine casing. By a still further aspect of the invention, the continuous groove in the composite base is dovetail shaped and arcuate in configuration, and the stressed member received therein has a compound arcuate configuration both along its length and in cross section.

While the invention is distinctly claimed and particularly pointed out in the claims appended hereto, the invention will be better understood and appreciated, along with other objects and features thereof, by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a sectional view of a gas turbine engine having compressor stator vane assemblies constructed in accordance with this invention;

FIG. 2 is a view -of a compressor stator vane assembly taken along viewing lines 22 of FIG. 1;

FIG. 3 is a pictorial view of one of the composite sectors comprising the stator vane assembly of FIG. 2;

FIG. 4 is a view taken along viewing lines 4-4 of FIG. 2 showing a stator vane and its discrete base portion;

FIG. 5 is a view of a stressed member in its unassembled, or unstressed, condition;

FIG. 6 is an enlarged view of the base portion of the stator vane of FIG. 4 illustrating the frictional engagement between the base portion and the stressed memher; and

FIG. 7 is a view similar to FIG. 6 showing a slightly modified arrangement.

Referring first to FIG. 1, a gas turbine engine 10 of the turbojet type is illustrated, the engine 10 having a generally cylindrical casing 11 enclosing, in axial flow relationship, an annular inlet duct 12, a compressor 13, a combustor 14, a gas generator turbine 15, and an annular exhaust nozzle or duct 16. The gas turbine engine 10 has a stator portion comprising the casing 11 and the other stationary structure including radial support struts 17 spanning the inlet duct 12 to provide rotor support means 18 at the front of the engine, a plurality of rows of radial compressor stator vanes 21, 22, 23, etc., the structure of the combustor 14, nozzle guide vanes 24 and 25 for the gas generator turbine 15, and radial support struts 26 spanning the exhaust nozzle 16 to provide rotor support means 27 at the aft end of the engine 10. The rotor portion of the engine 10 comprises the structure rotatably mounted on the support means 18 and 27 and as such includes a compressor drum 30 and a plurality of rows of compressor blades 31, =32, 33, etc., mounted thereon, turbine rotor discs 34 and 35 having rows of turbine buckets 36 and 37 mounted thereon, and a shaft 38 connecting the drum 30 and the rotor disc 34 and 35.

From FIG. 1 and the above description, it will be appreciated that the stator and rotor portions of the engine cooperate to form an annular motive fluid passageway 40 extending the entire length of the engine, the passageway 46 including at opposite ends of the engine 10 the inlet and exhaust ducts 12 and 16, respectively. In the illustrated gas turbine engine, the motive fluid which is initially air and then combustion products, is subject to several processes is it flows through the passageway 40. It is first compressed to high pressure in the compressor 13 and then burned at substantially constant pressure to produce high temperature exhaust gases which drive the gas generator turbine 15 where both the temperature and the pressure of the gases are reduced. Finally the low pressure, low temperature exhaust products are discharged at atmosphere through the exhaust duct 16. A turbomachine such as the gas turbine engine 10 is often thought of as a continuous flow machine through which the motive fluid flows in a completely uniform manner. In practice, however, the flow is generally far from uniform and smooth, particularly because of discontinuities introduced into the flow by the vanes, blades, buckets, and support struts extending across the annular passageway 40. As a result of such discontinuities, the various elements are subject to fluctuating aerodynamic forces which cause forced vibration. The compressor stator vanes 21, 22, 23, etc. are particularly susceptible to vibration caused in this manner. These aerodynamic forces are, of course, not the only cause of destructive vibration in a turbomachine. Even an extremely well balanced rotor portion can, when being run at thousands of-revolutions per minute, produce vibration in the stator portion as well as in the rotor portion. If vibration of this type is produced at certain resonant frequencies, vibration amplitudes and stress levels in the stator structure, particularly compressor stator vanes, can become quite large. The present invention provides improved and novel means for controlling such vibration.

With reference now to FIGS. 2 and 3, the annular row of non-variable or fixed angle vanes 21 is viewed in FIG. 2 from its upstream side, one of the composite sectors 45 comprising the stator vane assembly of FIG. 2 being illustrated pictorially by FIG. 3. As shown by FIG. 2,

the circumferential ends of the sectors 45 abut to form the complete 360 row of stator vanes 21. In the illustrated embodiment, there are twelve sectors 45 of 30 each, but it will occur to those skilled in the art that other numbers of sectors can be used, such as six 60 sectors. In general, any number of sectors may be used, down to a minimum number of two. In addition, each sector should contain a suflicient number of vanes to provide a suitable degree of wear resistance in accordance with the present invention; this requirement will become clear as this description proceeds.

As just described, the assembly, of stator vanes 21 includes a plurality of composite sectors 45. These sectors 45, are, however, substantially different than the sectors of certain prior art assemblies in that each stator vane 21 has a discrete base portion 46 formed integrally therewith, the circumferentially spaced vanes 21 projecting radially inward from the base portions 46 across the annular passageway. The abutting base portions 46 of each sector 45 form a composite base 47 which is, as best shown by FIG. 2, arcuate in configuration with respect to the longitudinal axis of the engine 10. Stated differently, the longitudinal axis of the engine 10, as viewed in FIG. 2, can be said to be the center of curvature of the composite base 47.

Referring now to FIGS. 3 and 4 each base portion 46 has a first lug 50 projecting axially upstream relative to the engine axis C and a second lug 51 projecting axially downstream, the first lugs 50 of each sector 45 being aligned to form a first composite, arcuate flange 50' and the second lugs 51 of each sector 45 being aligned to form a second composite, arcuate flange 51'. These composite flanges 50 and 51' are engaged by support means 52 which is an integral portion of the engine casing 11. More particularly, the support means 52 includes a first flange 53 projecting inwardly from the casing 11, the flange 53 defining an annular channel 54 opening in the downstream direction. The support means 52 further includes a second flange 55 spaced axially downstream of the first flange 53, the second flange 55 also projecting inwardly from the casing 11 and defining an annular channel 56 opening in the upstream direction. The channels 4, there is a small radial space 57 between the outer surfaces 58 of the assembled base portions 46 and the inner surface 59 of the casing 11.

In the. above description, it has been pointed out that a plurality of baseportions 46 cooperate to form a composite, arcuate base 47. To do this, means must be provided to hold the base portions 46 in abutting relationship. In accordance With the present invention, means is provided for frictionally engaging the base portions 46 comprising each base 47 to hold the base portions in abutting engagement to provide vibration damping. This arrangement will now be explained. With reference to FIGS. 2-4, each base ortion 46 has a recess 65 formed in its radially outer surface 58, the recess 65 being dovetail shaped in cross section and being circumferentially disposed with respect to the engine axis C. The recesses 65 in the abutting base portions 46 are aligned to form a continuous groove 66 extending the entire circumferential length of the composite base 47. As viewed in FIG. 2, the groove 66 is, as the composite base 47, arcuate with respect to the engine axis, or center of curvature C of the composite base 47.

The means frictionally engaging the base portions 46, is, as shown by FIG. 5, a spring member 70. With reference now to FIGS. 2-5, the spring member 70 is mounted in the arcuate groove 66 to provide the required frictional engagement. Since the member 70 extends the. entire length of the groove 66, its arcuate length L is substantially equal to the arcuate length of the groove 66. In addition, the curvature of the spring member 70 in its unstressed state is slightly greater than that of the groove 66; the reason for this will soon be apparent. In addition, the spring member 70 has in its unstressed condition an arcuate shape in cross section throughout its length. This arcuate configuration is superimposed on the arcuate configuration of the member 70 along its length. Stated differently, it can be said that the spring member 70 has a compound arcuate configuration.

In assembling the stator vane sector 45, the spring member 70, which has a width W greater than the width W of the widest part of the groove 66, assumes in cross section an arcuate shape, as shown by FIG. 4, having a curvature greater than that of its unstressed state. In assuming this new curvature in cross section, the spring member 7 0 straightens out along its length until the curvature along its length is the same as that of the groove 66. It will thus be obvious that the spring member 70 also has .a compound arcuate configuration in its assembled state When the stator vane sector 45 is assembled and supported in the compressor support means 52, the member 70 is a stressed member which, because of its resilience, wants to return to its unstressed configuration. Therefore, the member 70 exerts, as best shown by the embodiments of FIGS. 6 and 7, substantial forces F on the wall surfaces S of the groove 66 to maintain the bases 46 in abutting relationship. During engine operation, a substantial amount of energy can be dissipated through frictional rubbing between the stressed, spring member 70 and the base portions 46. In addition, the member 70 permits a limited amount of relative movement and rubbing between the lugs 50 and 51 and the channels 54 and 56 and between the abutting surfaces of abutting base portions 46. In this manner, significant levels of vibration damping can be attained. At the same time, however, the stressed member 70 imparts enough rigidity to the composite base 47 to provide substantially uniform wear along the support flanges 50 and 51. In other words, the stressed member 713 permits relative motion within a limited range, but, by transmitting moment and shear forces between adjacent base portions 46, does not permit the large relative motions normally associated with excessive wear.

It will now be obvious to those skilled in the art that the arrangement of this invention permits the turbomachine desinger to vary the amounts of vibration damping and wear resistance within substantial ranges. For example, by using a thin spring member 76, as illustrated by FIG. 6, a rather flexible vibration damping arrangement can be provided. If desired, a stiffer spring member 70 can be used as illustrated by FIG. 7, the spring member 70 of FIG. 7 having much greater thickness than the spring member of FIG. 6. This type of construction gives a more rigid vane sector 45 generally less subject to wear along its support flanges 50 and 51. Going even further in increasing rigidity, the member 70 may engage the inner surface 59 of the casing 11 as shown to bias the composite flanges 50' and 51' inwardly against the inner surfaces of the channels 54 and 56 respectively.

In the foregoing description, the means for frictionally engaging the base portion 46 is a spring member 70 received in a dovetail shaped groove 66. It will readily occur to those skilled in the art that other stressed elements can be used to perform this function. Similarly, it will be obvious that the invention may be used relative to nonvariable turbine nozzle vanes and rotor blades and buckets in addition to the illustrated compressor stator vanes.

From the foregoing, it will be appreciated that the improved non-Van'able vane assembly of this invention provides a composite sector arrangement having superior vibration damping in combination with a high degree of wear resistance. In addition, since each vane and its base portion are manufactured separately, the arrangement or this invention has the manufacturing and maintenance advantages of the individual base type of stator construction while still having the ease of handling characteristics of the sector type of stator construction.

While particular embodiments of the invention have been shown and described, it will be understood that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended to cover all such changes and modifications by the appended claims.

What is claimed as new and is desired to secure by Letters Patent of the United States is:

1. A stator assembly for use in a turbomachine having an axial flow passageway extending between axially spaced upstream and downstream ends thereof, said stator assembly comprising:

a row of circumferentially spaced, radial stator vanes,

said row comprising at least two stator vane sectors;

each of said stator vane sectors comprising: a plurality of vanes each having a discrete base portion formed integrally therewith at radially outer end thereof, said base portions disposed in abutting relationship to form a composite base having an arcuate configuration relative to the axis of said turbornachine;

and means frictionally, resiliently and continuously engaging said base portions to maintain said base portions in abutting relationship and to provide vibration damping;

and means engaging said composite bases to support said row of stator vanes in said axial flow turbomachine.

2. A vane sector as defined by claim 1 in which each of said base portions has a recess therein, said recesses being aligned and forming a continuous arcuate groove in said composite base, and in which said means frictionally engaging said base portions comprises a stressed member resiliently mounted in said arcuate groove.

3. A stator assembly as defined by claim 2 in which said groove in said composite base has a dovetail shaped configuration in cross section.

4. A stator assembly as defined by claim 3 in which said stressed member in its unstressed state has a length substantially equal to the arcuate length of said groove and a width greater than the width of said groove, assembly of said stressed member in said groove causing said stressed member to assume a compound arcuate configuration both along its length with respect to the axis of said turbomachine and in cross section, the arcuate configuration along its length being the same as the arcuate configuration of said groove.

5. A stator vane assembly as defined by claim 4 in which each of said base portions has a first lug projecting axially upstream and a second lug projecting axially downstream, the first lugs of each stator vane sector being aligned to form a first composite flange and the second lugs to each stator vane sector being aligned to form a second composite flange, said support means engaging said first and second composite flanges to support said row of stator vanes in said axial flow turbomachine.

6. A stator vane assembly as defined by claim 5 in which said support means includes first and second annular, axially spaced channels, said first annular channel opening in the downstream direction and receiving said first composite flanges and said second annular channel opening in the upstream direction and receiving said second composite flanges.

7. A stator vane assembly as defined by claim 6 including a substantially cylindrical casing surrounding said row of vanes, said support means being an integral portion of said casing.

8. A stator vane assembly as defined by claim 7 in which said stressed member engages said casing to bias said first and second composite flanges against the radially inward surfaces of said first and second annular channels respectively.

References Cited UNITED STATES PATENTS 1,165,005 12/1915 Herr 253-77 2,265,592 12/1941 Allen 253-77 2,654,566 10/1953 Boyd et al. 253-78 2,669,383 2/1954 Purvis et al. 253-77 X 2,847,187 8/1958 Murphy 253-77 2,945,290 7/1960 Walsh 253-78 X 2,971,743 2/1961 Welsh 253-77 3,034,764 5/1962 Davis et al. 253-77 FOREIGN PATENTS 797,521 7/ 1958 Great Britain.

MARTIN P. SCHWADRON, Primary Examiner. EVERE'ITE A. POWELL, JR., Examiner. 

1. A STATOR ASSEMBLY FOR USE IN A TURBOMACHINE HAVING AN AXIAL FLOW PASSAGEWAY EXTENDING BETWEEN AXIALLY SPACED UPSTREAM AND DOWNSTREAM ENDS THEREOF, SAID STATOR ASSEMBLY COMPRISING: A ROW OF CIRCUMFERENTIALLY SPACED, RADIAL STATOR VANES, SAID ROW COMPRISING AT LEAST TWO STATOR VANE SECTORS; EACH OF SAID STATOR VANE SECTORS COMPRISING: A PLURALITY OF VANES EACH HAVING A DISCRETE BASE PORTION FORMED INTEGRALLY THEREWITH AT RADIALLY OUTER END THEREOF, SAID BASE PORTIONS DISPOSED IN ABUTTING RELATIONSHIP TO FORM A COMPOSITE BASE HAVING AN ARCUATE CONFIGURATION RELATIVE TO THE AXIS OF SAID TURBOMACHINE; 